In accordance with advanced technologies to further scale down physical dimensions of semiconductor devices, a size of a respective interconnect line (e.g., a metallization structure) in a interconnect level (e.g., a metallization layer), coupled to the semiconductor device, tends to scale down accordingly. Furthermore, in order to connect more semiconductor devices on a wafer with a limited area, interconnect lines across various interconnect levels are electrically connected in a three-dimensional fashion by vertical conductive via structures.
In general, a via structure is typically formed by depositing a dielectric layer over a lower metallization (i.e., conductive) structure, recessing through the dielectric layer to form a vertical trench or hole, also known as a via hole, so as to expose a portion of a top surface of the lower metallization structure, and then refilling the via hole with a conductive material, e.g., metal materials. The via structure then can be used to electrically couple the lower metallization structure to one or more higher metallization structures. As such, an electrical connection path through the conductive metal material in the via hole is formed from the lower metallization structure to the higher metallization structure.
Before refilling the via hole with the metal material to form a via structure, a cleaning process is typically performed to remove residuals (e.g., polymer and/or photoresist material) distributed over the via hole, which may be induced prior to, subsequently with, or subsequent to the formation of the via hole. However, this cleaning process, which is typically based on an acid solution, may cause one or more undercuts in the lower conductive structure. Such undercuts make it relatively difficult to completely refill the via hole with the metal material during a subsequent metallization process since the undercuts create voids that remain unfilled after the metallization process. The voids formed along the electrical connection path may cause various issues, particularly when a current flows through the electrical connection path. For example, due to the presence of the void(s), an effective cross-sectional area for the current to flow may be reduced, which may in turn increase a corresponding current density. Further, continuously increasing the current density may further increase a size of the void, which may ultimately cause the electrical connection path to become an open circuit.